1. Field of the Invention
The present invention relates to a camera with a shake preventing apparatus.
2. Related Background Art
As a conventional camera with a shake preventing apparatus, a single-lens reflex camera with a single focal point exchangeable lens having a shake preventing optical system for preventing an image blur on an image plane by decentering a lens group immediately after an aperture stop is known.
In this exchangeable lens, a driving mechanism and an actuator for decentering a shake correction lens are arranged behind the aperture stop.
However, the conventional camera with the shake preventing apparatus poses the following problems since the driving mechanism and the actuator for decentering the shake correction lens are arranged on a base behind the aperture stop.
Upon application to a lens shutter camera with a zoom lens, since a lens shutter unit is moved in the optical axis direction according to a zooming operation, a unit with the driving mechanism and actuator for the shake correction lens must be able to be moved in the optical axis direction according to the zooming operation, resulting in a complicated structure, an increase in size of the camera, and high cost.
Since the actuator for decentering is arranged, the diameter of a lens barrel is increased accordingly, resulting in an increase in size of the camera.
FIG. 8 is a perspective view showing a shake correction apparatus, and FIGS. 9A and 9B are charts showing an optical system of a photographing lens.
A camera shown in FIG. 8 has a camera main body 116, a photographing lens barrel 117, a distance-measurement window 118, a finder window 119, and a release button 120.
The camera body 116 includes angular speed sensors 105 and 106. With reference to the principal point H of the photographing lens barrel 117, the angular speed sensor 105 detects an angular speed of rotation of the camera main body 116 about the Y axis, and the angular speed sensor 106 detects an angular speed of rotation of the camera main body 116 about the X axis. The shake correction apparatus obtains the direction and speed of an image blur on an imaging plane 143 on the basis of the angular speed data detected by the angular speed sensors 105 and 106.
An optical system shown in FIGS. 9A and 9B comprises a 2-group zoom lens. Convex lenses L1 and L2 constitute a first lens group, and a concave lens L3 constitutes a second lens group. FIG. 9A shows a wide-end state, and FIG. 9B shows a telephoto-end state.
The convex lens L2 is used as a shake correction lens (to be referred to as a shake correction lens L2 hereinafter), and is shifted in a direction of an arrow A on the basis of the direction and speed data of the image blur on the imaging plane 143. Appropriate shift direction and amount are selected to correct the image blur on the imaging plane 143.
The convex lens L1 is a focusing lens, and is moved in a direction of an arrow B to perform a focusing operation. Note that sectors of a lens shutter are designated by 140 and 141.
The shake correction apparatus described above starts a shake correction operation simultaneously with the start of exposure, when a main switch is turned on, or when a release button is depressed to its half-stroke position. For this reason, the following problems are posed.
1 When the shake correction operation is started simultaneously with the start of exposure, the shake correction operation cannot be precisely performed due to the influence of the inertia of the shake correction lens and its driving system.
FIG. 7A is a graph showing the relationship among the time, a shake amount R, and a correction amount C when the shake correction operation is started simultaneously with the start of exposure.
In FIG. 7A, a solid line represents the detected shake amount R, and a broken curve represents the correction amount C. The shake correction apparatus shifts the shake correction lens L2, so that a correction amount .DELTA.1 becomes equal to a shake amount .DELTA.0 indicated by a solid line after the end of exposure. However, the correction speed is insufficient in the early stage of correction, as indicated by a broken curve in FIG. 7A, due to the influence of the inertia of the shake correction lens L2 itself or a driving mechanism for driving the lens L2.
Therefore, the shake amount .DELTA.0 within the exposure time becomes a correction amount .DELTA.1 smaller than the amount .DELTA.0, and the shake correction operation cannot be precisely performed.
2 When the shake correction operation is started when the main switch is turned on or when the release button is depressed to its half-stroke position, a shake correction state can be confirmed through a finder in a single-lens reflex camera. However, in a compact camera, since the photographing screen is not directly observed, the shake correction state cannot be confirmed, and electric power is consumed even during this interval, thus shortening the service life of a battery.
In addition, photometry and distance-measurement operations must be simultaneously performed, and the processing capacity of a control circuit must be increased by that for the shake correction.
Currently manufactured cameras have remarkable electronic functions such as an auto-exposure mechanism, an auto-focus mechanism, and the like, and can perform highly automated operations. However, a camera of this type cannot provide a sufficient automatic function as a countermeasure against an image blur due to a camera shake, which occurs in a hand-held photographing state. For a conventional camera of this type, the proposals to be described below have been made.
The proposals will be briefly described below. When a proper photographing operation is to be performed, the influence of, e.g., a camera shake at the side of a photographer who holds the camera must be taken into consideration. Thus, a shake detection means is arranged, and an alarm display of a shake state is made on the basis of the detection result under a condition that a shake occurs.
A technique for performing control on the basis of the detection result of shake detection means to inhibit a photographing operation under a shake occurrence condition is also proposed in, e.g., U.S. Pat. No. 4,901,096.
Furthermore, in still another proposal, a camera is mounted on an anti-shake base which can absorb an external vibration, thereby eliminating the influence of a shake.
In still another proposal, a gyro for generating an inertia is attached to a camera.
However, the above-mentioned conventional countermeasures against an image blur cannot avoid the following problems.
When only an alarm display of a shake state is made, a photographer can confirm a camera shake. However, the camera shake cannot be directly avoided, and a photographing operation free from an image blur cannot be performed.
When a photographing operation is inhibited in a camera shake state, the photographing condition is limited, and a photographer may lose a shutter chance.
Furthermore, when the anti-shake base or the gyro is utilized, not only the entire size is increased, but also cost is increased. Thus, such a structure is not suitable for a compact camera using a 35-mm film.
For this reason, an apparatus for movably controlling a portion of an optical system as a correction optical system according to the detection result of the above-mentioned shake detection means so as to prevent an image blur on a film imaging plane as much as possible is also proposed. However, this correction mechanism has a complicated structure, and makes the entire structure bulky. In addition, this apparatus suffers from a problem upon movable control of the correction optical system in a desired state. Thus, it is demanded to take some countermeasure for solving all these problems.
As a shake correction apparatus, for example, the following apparatus is known. That is, angular speed sensors are provided to a camera main body or a lens, and angular speeds in the X- and Y-directions are detected by the angular speed sensors, as shown in FIG. 8. The direction and speed of an image blur on the imaging plane are obtained based on the detected angular speeds, and a shake correction lens is shifted according to the obtained direction and speed.